Dissipative energy loss within the left ventricle detected by vector flow mapping in children: Normal values and effects of age and heart rate

BackgroundVector flow mapping (VFM) is a novel echocardiographic technology which enables visualization of the intraventricular flow velocity vector. Dissipative energy loss (EL) derived from the velocity vector field of intraventricular blood flow is considered to reflect the efficiency of blood flow, and could be an indicator of left ventricular function. We aimed to determine the reference values of the EL derived from VFM within the left ventricle.MethodsVFM analysis was performed using echocardiography in 64 healthy children. The velocity vector fields of the intra-left ventricular blood flow were obtained from the apical 5-chamber view, and the EL values during systole and diastole were calculated. The measurements were averaged over three cardiac cycles, and indexed to body surface area (BSA).ResultsThe mean subject age was 6.8 ± 4.3 years. The mean EL was 4.10 ± 2.35 mW/m/m2 BSA during systole and 16.24 ± 11.63 mW/m/m2 BSA during diastole. On multivariate analysis, age and heart rate (HR) were independent predictors of systolic EL, whereas age, HR, and E wave peak velocity were independent predictors of diastolic EL. The regression equations used to predict the BSA-indexed systolic and diastolic EL were as follows: log10 (systolic EL) = −0.0332 − 0.00213 × age (months) + 0.00789 × HR (beats/min) (adjusted R2, 0.833; p < 0.0001); and log10 (diastolic EL) = 0.277 − 0.00346 × age (months) + 0.00570 × HR (beats/min) + 0.00564 × E wave peak velocity (cm/s) (adjusted R2, 0.867; p < 0.0001).ConclusionsThe systolic and diastolic EL were positively correlated with HR and negatively correlated with age. Moreover, the diastolic EL was positively correlated with the E wave peak velocity. The present study provides reference values for the systolic and diastolic EL that can be used in future studies examining patients with heart disease.